1. Field of the Invention
The invention relates to a power transmission apparatus for a vehicle, which includes an electric differential portion in which a difference between the rotational speed of an input shaft connected to a main power source and the rotational speed of an output shaft is controlled by controlling the operating state of a motor connected to a rotational element of a differential mechanism. More specifically, the invention relates to a technology in which if a shift position is changed from a parking position to a neutral position while executing a control that starts or stops the main power source, a control that changes the load of the main power source, or the like, a decrease in starting performance/stopping performance of the main power source, and deterioration of noise/vibration characteristics (NV characteristics) are suppressed.
2. Description of the Related Art
A power transmission apparatus for a vehicle, which includes an electric differential portion, is available. In the electric differential portion, a difference between the rotational speed of an input shaft connected to a main power source and the rotational speed of an output shaft is controlled by controlling the operating state of a motor connected to a rotational element of a differential mechanism. An example of the power transmission apparatus for a vehicle is a drive apparatus for a vehicle described in Japanese Patent Application Publication No. 2005-264762 (JP-A-2005-264762). In the publication JP-A-2005-264762, the electric differential portion mainly includes a planetary gear unit, a first motor, and a second motor. A sun gear of the planetary gear unit is connected to the first motor. A carrier of the planetary gear unit is connected to an engine (the main power source). A ring gear of the planetary gear unit is connected to the second motor. It is possible to control the rotational speed of each rotational element of the planetary gear unit, by controlling the first motor and the second motor. The publication JP-A-2005-264762 also describes a technology in which the main power source is quickly started by quickly increasing the rotational speed of the main power source to an ignition rotational speed at which ignition can be performed, using the second motor and/or the first motor.
In the power transmission apparatus for a hybrid vehicle, which includes the electric differential portion, for example, the power transmission apparatus described in the publication JP-A-2005-264762, when the shift position is the parking position, a load operation of the main power source, an idling operation of the main power source, or the like is performed, for example, to start/stop the main power source, or to generate electric power. To appropriately control the load operation of the main power source, the idling operation of the main power source, or the like, a fixing control that fixes the output shaft of the electric differential portion using the second motor is executed When the shift position is the neutral position, the main power source is not started/stopped, and the load operation of the main power source is not performed. That is, when the shift position is the neutral position, the fixing control that fixes the output shaft of the electric differential portion using the second motor is not executed.
In the drive apparatus for a vehicle described in the publication JP-A-2005-264762, for example, if the shift position is changed from the parking position to the neutral position while executing the control that starts or stops the main power source, the fixing control using the second motor ends. Therefore, the second motor is rotated, and the starting performance and the stopping performance of the main power source may decrease. Also, if the shift position is changed from the parking position to the neutral position while the load operation of the main power source is being performed, the rotational speed of the main power source may fluctuate due to the rotation of the second motor, and the noise/vibration characteristics (NV characteristics) may deteriorate. A method has not been devised to suppress the decrease in the starting performance and the stopping performance of the main power source, and the deterioration of the noise/vibration characteristics if the shift position is changed from the parking position to the neutral position while the main power source is being started or stopped, or the load operation of the main power source is being performed.